The Grand Duke Canal was constructed to drain the water from the Pian del Lago 156 hectares of which used to become flooded to a depth of 3 meters with stagnant water each winter. In the dry season the water formed a lake of 93 hectares which gave its name to the plain, hence: Pian del Lago (Plane of the Lake). The expansion and contraction of the flooded area would continually make organic materials, plants, and insects, putrefy, rendering the whole surrounding area unhealthy, especially in the summer.* For this reason the friars of the monasteries of San Leonardo and Belriguardo would transfer to a monastery in Pontignano in the summer, and in the winter return to their respective monasteries.
Also, the entire area bordering the lake used to be abandoned and uncultivated because the farmers who had been taken ill could not continue to live there. The unhealthiness caused the zone to be deserted all the way to the Augustinian monastery of Lecceto, and to Celsa, San Colomba, Fungaia, Fornacelle, Chiocciola, and Abbadia a Quarto.
The canal was mostly the work of a Sienese gentleman, Francesco Sergardi Bindi, who in the enterprise of draining the land--considered a folly by his contemporaries--consumed his entire fortune, 37,000 scudi. The work of constructing the underground drainage canal, in which the entrance was located in the plane between the Casalino and Osteriaccia estates, and the from outlet on the Rigo stream the water would join the Serpenna, in Rosia, and then flow into the Merse river, was long and difficult. Begun in 1766, it was largely completed in 1774. Because of the extremely hard rock the builders used a total of 18,577 (Sienese) pounds of blasting powder. More than once arguments over property lines among the abutting owners interrupted the work as did floods caused by the rains (which were disastrous on 21 December 1770).
The quality of the work was not exactly flawless, thus rendering the project the object of complaints to Grand Duke Leopold I. The abutters turned to the Grand Duke because it was no longer possible for Bindi to finance the necessary improvements. The "enlightened" Grand Duke, who himself in these years had enacted a centralized policy of improving the condition of peasants and of reclaiming wetlands throughout his state, had the canal lengthened by 197 meters (bringing it thus to 2,173 meters overall), and added piers to better support the brick vaults, and paved the bottom. Unfortunately, whereas traces of the Grand Duke's intervention remain quite visible, with the marble obelisk over the entrance crediting him for the entire enterprise, almost nothing remains to commemorate the Sienese noble's meritorious work.
By the beginning of 1781 the work was definitely finished and as such was consigned to the Collegio di Balìa, to the engineer Bernardino Fantastici, assistant to the Director of Public Works, the mathematician Pietro Ferroni, and the treasurer Cosimo Cennini, nominated by the same bureau. . . .

Reproduced with permission, from: Ermanno Vigni, "A pesca in Pian del Lago," in Il Carroccio 47, (September/October 1993).

* Translator's note: Until the twentieth century people explained the apparent unhealthiness of swampy areas with ideas of "putrification" and similar notions. The unhealthiness was more likely due to the ideal habitat wetlands provided for malaria-bearing mosquitoes or the greater likelihood of contact with a water-born parasite or disease. Regardless of the explanation, farmers and the monks were wise to avoid flooded areas in the summer.